Which sequence correctly describes the general penetrant testing procedure?

• A. Pre-clean, dry, apply penetrant, dwell time, remove excess penetrant, dry, apply developer, dwell, interpretation, evaluation, post-clean
• B. Pre-clean, dry, apply penetrant, dwell, dry, remove excess, apply developer, post-clean, interpretation, evaluation
• C. Dry, pre-clean, apply penetrant, dwell, remove excess penetrant, dry, apply developer, dwell, interpretation, evaluation, post-clean
• D. Pre-clean, dry, apply penetrant, dwell time, remove excess penetrant, dry, apply developer, dwell time, interpretation, evaluation, post-clean

Answer: (D)

This question tests understanding of the proper sequence of steps in liquid penetrant inspection. The surface must first be cleaned so oils and contaminants are removed, and drying is done before applying penetrant to ensure good wetting and penetration. After applying the penetrant, a dwell time allows it to seep into any surface-breaking flaws. Then excess penetrant is removed to avoid background staining that can hide or obscure indications. A subsequent drying step is needed before applying the developer so the developer can perform correctly without interference from surface residues. After developer application, a dwell time lets the developer draw penetrant out of flaws to form visible indications. Finally, interpretation and evaluation follow, with post-clean to remove residual penetrant and developer.

If drying or dwell timings are misplaced, indications can be masked, blurred, or misinterpreted, which is why this sequence aligns with how penetrant inspection reliably reveals flaws.